Active matrix liquid crystal displays include a matrix of pixels that each include red, green and blue cells. Each cell has a transistor that controls the operations of the cell. Cells in the same line of the display typically have the gate electrode of their transistors commonly connected by a gate line. Cells in the same column typically have their source electrodes commonly connected by a source line. Thus, each cell of each pixel may be individually addressable through selection of a gate line and a source line.
Information to be displayed by the liquid crystal display is typically provided as a digital value that is converted to an analog signal to drive a source line. Conventionally, a separate buffer is provided to drive each cell source line for the liquid crystal display. An example of a conventional source driver circuit 100 for three cell sources lines of a column of pixels is illustrated in FIG. 1. As seen in FIG. 1, digital data, such as 18 bit digital data, provides a red value (e.g., 6 bits) DATA_R, a green value (e.g., 6 bits) DATA_G and a blue value (e.g., 6 bits) DATA_B. The digital data is converted to a corresponding analog value R_VOL, G_VOL and B_VOL by respective digital to analog converters DR, DG and DB. The analog values are driven onto lines of a display panel, such as source lines in a liquid crystal display (LCD) panel, by buffers R_BUF, G_BUF and B_BUF to provide red, green and blue drive voltages ROUT, GOUT and BOUT. Typically, each source line of a display will have its own driver circuit as illustrated in FIG. 1 and these drivers are typically all in an on-state during operation of the LCD panel, thereby, consuming power.
FIG. 2 is a further illustration of a conventional source line driver circuit for a LCD display that includes selective switching of connectivity to buffers so as to reduce the number of leads needed to test the circuit. By providing the switches GRAY_ON and CH_MUX, a single lead may be selectively connected to the buffer amplifier 10 and the buffer amplifier 20 for test purposes. Furthermore, the buffer amplifiers 10 and 20 also may be disabled for test purposes by the signal AMP_ON/OFF.